1. Field of the Invention
The invention concerns the field of reaction injection molded polyurethanes.
2. Description of the Prior Art
Reaction Injection Molding (RIM) is a technique for the rapid mixing and molding of large, fast curing urethane parts. RIM polyurethane parts are used in a variety of exterior body applications on automobiles where their light weight contributes to energy conservation. RIM parts are generally made by rapidly mixing active hydrogen containing materials with polyisocyanate and placing the mixture into a mold where reaction proceeds. These active hydrogen containing materials comprise a high molecular weight polyhydric polyether and a low molecular weight active hydrogen containing compound. After reaction and demolding, the parts may be subjected to an additional curing step which comprises placing the parts in an ambient temperature of about 250.degree. F. or greater.
In a previously filed patent application, Ser. No. 136,199 filed Apr. 1, 1980, and now U.S. Pat. No. 4,273,885, issued June 16, 1981, a catalyst system for RIM polyurethane elastomers was described which was comprised of dimorpholinodiethylether, dibutyltin dilaurate and an alkyl tin mercaptide. The catalyst combination in that patent application imparts superior processing characteristics to RIM polyurethane elastomer systems. However, we have since discovered that the use of dimorpholinodiethylether, while advantages in many RIM systems, interferes in the cure of certain important paint systems known as high solids enamel paints. Methods for solving this problem are the subject of other patent applications. See, for example, Applications Ser. Nos. 268,460, 268,528 and 268,459 filed on May 29, 1981.
In the present invention we have discovered that the use of a high molecular weight amine based polyol as part of a urethane catalyst combination provides the advantage of not interfering in the urethane network as do reactive amines of low molecular weight. Thus these catalysts do not substantially interfere with the properties of the urethane polymer and do not migrate from the finished urethane product, as is the case for low molecular weight unreactive amine catalysts.
A general discussion of catalysis by soluble polymers is described in The British Polymer Journal, 12, 70 (1980) by D. C. Sherrington.
Application Ser. No. 268,220 filed on May 29, 1981 discloses and claims a catalyst comprising polymers containing tertiary amine moieties. We have discovered that the use of amine based polyols in the preparation of RIM elastomers serve also as catalysts for the reaction without releasing harmful amine to the surface. The use of these amine based polyols allows the finished RIM parts to be painted with high solids enamels.